If I walk far enough away from a map-in-item-frame such that the chunk it's in unloads, when I walk back, sometimes it's gone. All the other blocks in the chunk pop back into existence, but not the map or frame themselves. When I say "gone" I mean that it's totally invisible, and punching or clicking the area where the map is supposed to be does nothing as though there was nothing there- I can't pull the map off the frame or punch it off the wall. The only way to get the map back is to destroy the block that the item frame was attached to. This problem is semi-permanent in the sense that once it happens, it never reappears again unless I completely close out of the map back to the main menu and then log in again. (Manually reloading chunks/textures/etc through the F3 debug options has no effect).

Note: this bug is hard to reproduce. It only happens maybe one out of every five or ten times I load a map, and only on certain maps. In testing, I created a bunch of superflat worlds and got it to happen on two of them fresh on creation, so it's not a case of old maps or file corruption.